Objective. To study lumbopelvic pain in women randomized to a regular exercise program during pregnancy compared to women receiving standard antenatal care. Design. A two-armed, two center randomized controlled trial. Setting. St. Olavs Hospital Trondheim University Hospital and Stavanger University Hospital. Population. A total of 855 pregnant women were randomized to intervention or control groups. Methods. The intervention was a 12-week exercise program, including aerobic and strengthening exercises, conducted between 20 and 36 weeks of pregnancy. One weekly group session was led by physiotherapists and home exercises were encouraged twice a week. Controls received standard antenatal care. Main Outcome Measures. Self-reports of lumbopelvic pain and sick leave due to lumbopelvic pain. The data were analyzed according to the "intention-to-treat" principle. Results. There were no significant differences between groups of women reporting lumbopelvic pain at 36 weeks (74% vs 75%, p= 0.76). The proportion of women on sick leave due to lumbopelvic pain was lower in the intervention group (22% vs 31%, p= 0.01). Conclusion. Exercise during pregnancy does not influence the prevalence of lumbopelvic pain, but women offered a regular exercise course seem to handle the disorder better.